Manufacture of vacuum tubes



July 3, 1934. EDELMAN 1,964,978

MANUFACTURE OF VACUUM TUBES Filed Oct. 4, 1929 for use.

Patented July 3, 1934 UNITED STATES PATENT OFFEQE Philip E. Edelman, Chicago, 111., assignor, by mesne assignments, to Robert T. Mack, trustee,

Chicago, 111.

Application October 4, 1929, Serial No. 397,250

8 Claims.

An object of this invention is to provide a more complete cleaning up or elimination of residual or entrained gases from the elements employed in the vacuum tube. This invention is particularly suited for the manufacture of alternating current type tubes, and especially screen grid type thermionic vacuum tubes.

In the manufacture of screen grid vacuum tubes, for example, difficulty is experienced in removing entrained gases occluded in the metal parts employed in the structure used. The method of applying heat by application of a high frequency field of force to the metal parts during the exhaustion of the vacuum tube envelope, while eifective for other types of vacuum tubes, is not satisfactory in the case of a screen grid type tube because the interior metal parts which also contain entrained or occluded gases are shielded from the effect of the high frequency field of force by the exterior metal parts, namely, the plate and/or the shield grid element. Failure of manufactured screen grid tubes has been analyzed, and neglecting actual mechanical defects or short circuits in which metal parts touch each other as a result of injuries in transit or weak supporting structure, it is found that screen grid tubes tend to become gassy or defective in operation because of incomplete cleaning of gases from the metal parts during manufacture.

I have conceived thata practical solution of this problem is to successively or simultaneously electronically bombard all of the metallic elements of the vacuum tube during exhaustion of the envelope, in which said metal parts are mounted Preferably, I accomplish this by connecting all of the metal elements, the cathode, the grid, the screen grid, and the plate successively or simultaneouslyto successively tapped sources of potential sufiiciently high in voltage to cause said metal elements to serve in a rectifier thermionic relation, thereby causing them to heat. Thus the grid and screen grid respectively are in effect made to serve in the dual role of cathode and anode action during completion of exhaustion of the envelope in which the said metal parts are contained. Said metal parts thereby become heated sufiiciently to drive off entrained or occluded gases therein, and the electron emission simultaneously applied assists in forcing the ionized gas content free from the heated metal parts. The new method affords rapid and substantially complete cleaning of entrained or occluded gases from the assembled metal parts, as well as complete manufacturing control thereof during the processing or final exhaustion of the vacuum tube.

I am illustrating an exemplification of my invention in the accompanying drawing, which is a diagram of a vacuum tube and the means employed to clean gases from the metal parts thereof during final exhaustion of the envelope of the vacuum tube.

Referring to the figure, a vacuum tube provided with envelope 1 has a main seal support 14 which carries filament F-F, cathode C, grid G, screen grid S and plate P in any customary manner. An exhaust tube 2 may be provided for envelope 1 at the screen grid seal terminal 13 and attached to pump exhausting equipment 3 provided with an exhaust gauge 4 in a well known manner.

Envelope 1 is shown before a base terminal is applied thereto, and has connecting terminal wires 12 for its respective metal element parts F, G, P, C, S. A plurality of separate current meters 5, 5 are provided in series with control switches 6, 6, and respectively connected to terminals 12 of the vacuum tube 1, as shown, so as to receive different potentials from the tapped secondary winding of the transformer 8. The primary coil 9 of the transformer 8 is connected to a source of alternating current 10 by means of a switch 11.

The transformer secondary winding 7 heats the cathode filament F, causing electrons to be emitted from the cathode surface C when the envelope 1 is nearly completely exhausted by the pump device 3. The grid G is connected, as shown, to a sufficiently higher tap on the winding 7 of the transformer 8, so that, with respect to cathode C, the grid G is connected as an alternating current rectifier and sufiicient current is passed to grid G to heat it. Similarly, the screen gird S is connected to a higher potential tap on the winding 7, so that it is connected for rectifier action with respect to the cathode C and/or the grid G (when G is heated) and itself becomes hot. This is repeated for plate P, a higher tap on the transformer winding 7 being used so that P serves for rectifier action with respect to the elements C, G, S, respectively.

The meters 6, 6, show the action and the completion of the same. Also the operator may observe presence or absence of visible gas glow in the envelope 1 during the exhausting operation. I prefer to successively operate the switches 6, 6, for the stated result, but may also operate all of said switches simultaneously by selecting proper taps on the transformer winding '7 for this purpose. Since the operation aforesaid is made near the completion of exhaustion of envelope 1, substantially all residual entrained or occluded gases of the metal parts F, C, G, S, P, are efiectively driven out and exhausted from envelope 1 by the pump 3. In lieu of the transformer 8, I may employ a tapped source of direct current for the same purpose. On completion of the said cleaning action, the tube portion 2 may be sealed in a well known manner by applying a flame thereto. Other screen elements as used in more complicated screen grid arrangements are treated in the same way.

While I have shown and described but a few embodiments of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made which do not depart from the spirit and scope of the invention as disclosed in the appended claims.

I claim:

1. In the manufacture of a vacuum tube having a plurality of metal and grid elements therein, the step which consists in applying a source of alternating electrical current to each of said elements at different operating potentials during the final exhaustion of said vacuum tube to cause the occluded gas in said elements to be driven off, the current to each metal element being automatically limited so that if any one of said elements receives more than its proportion of the total current, the current supplied to the other elements is correspondingly reduced in a manner tending to restore correct proportionment of the said currents.

2. In the manufacture of a vacuum tube having a plurality of grid elements, the step which consists in simultaneously exhausting said vacuum tube and applying to each of said elements a source of alternating current from a common transformer so that if any one element draws excessive current therefrom the current to the other elements is reduced with tendency to control said excessive current, said elements to be heated to a point at which occluded gas will be expelled.

3. In the manufacture of a vacuum tube of the screen-grid type having a heater element, a cathode, a grid, a screen grid, and a plate, the step which consists in simultaneously exhausting said vacuum tube and applying alternating electrical current severally but dependently limited to said heater element, cathode, grid, screen grid and plate, characterized by the fact that successively higher operating potentials are applied respectively to these members as they are located more remote from the heater element.

4. In the manufacture of a vacuum tube having a plurality of metallic and grid elements therein, the step which consists in exhausting said vacuum tube while a plurality of different potentials are applied to said elements from a common self-regulating tapped transformer output connected for rectifier action with respect to said elements so that excessive current drawn by any one element reduces the current supplied to the others and tends to restore the current to said one element to a normal amount, and completing the exhaustion after said elements have become heated by current supplied by said transformer to a point at which the occluded gases are driven off.

5. In the manufacture of a vacuum tube having a plurality of electrode elements, the step which consists in simultaneously exhausting said vacuum tube and applying switching a plurality of diiferent alternating current potentials from a self-regulating source to said elements to heat same and drive occluded or entrained gases therefrom, the current supplied to each electrode element being automatically proportioned with respect to the current supplied to the others at the same time in a manner tending to restore uniform current supply to each electrode element.

6. In the manufacture of a vacuum tube having a cathode, control electrodes, and an anode, the step which consists in exhausting said tube while a plurality of alternating currents are applied to said electrodes from a common self-regulating source of limited total output, varying the rectified current between each electrode and said cathode and switching same to progressively obtain electron bombardment and heating of each said electrode, thereby controlling the current supplied to each electrode to a predetermined limit finally maintained by said common regulating source upon completion of the exhaustion.

'7. In the manufacture of a vacuum tube having a cathode, control electrodes, and an anode, the step which consists in exhausting said tube while alternating currents are applied to said electrodes from a common transformer of limited total output in manner operating each said electrode as a rectifier with respect to said cathode and heating same to remove occluded gasses therefrom, this operation being controlled both by switching and variation of applied potentials to each electrode and further automatically regulated by said transformer so that excessive current drawn by any one electrode causes reduced current to be supplied to said cathode, thereby tending to reduce the excessive current to an amount which will not cause deterioration of said electrode which temporarily receives excess current.

8. In the manufacture of a screen grid type vacuum tube having a heater element, a cathode,

a grid, a screen grid, and an anode, the step which consists in simultaneously exhausting said vacuum tube and applying self-regulated alternating currents of limited total output to said heater element, cathode, grid, screen grid and plate under control of switching means to vary said currents separately, of potential varying means for each separately, and of current limiting regulation tending to restore a normal balance on said currents drawn upon completion of exhaustion of the tube.

PHILIP E. EDELMAN. 

